uhm...
Should be better a way to empty all resources.
Like the ability to mark "obsolete" a depot and FUEL DRON and TRASPORT DRONE try to take all avaiable resorces from obsolete depot to other respective depots (FUEL, LIQUID, GOODIESS etc...). May be with a number of try to found an avaibale depot and then stop to search the avaiable depot for that resource.